All the NeoMyth cart menus have SDIO support for SD/SDHC cards. SDIO is using the 4-bit parallel access of the SD card rather than the serial most interfaces use. It's easier to do on "lesser" systems since it just needs GPIO to the SD card. All the NeoMyth menus are open source and found here:http://code.google.c.../neo-myth-menu/

The N64 menu uses C code everything but the main data transfer loop when reading sectors. The current code can detect and initialize an SD card in less than a second.